1. Field of the Invention
The present invention relates to a clutch mechanism for a vehicle seat.
2. Description of the Related Art
A related-art clutch mechanism for a vehicle seat is described in JP-A-200-95237. This vehicle seat includes a seatback and a headrest body supported above the seatback. The seatback includes therein an acceleration detecting mechanism, and a movement detecting mechanism which detects a movement of a passenger. Specifically, the movement detecting mechanism includes a detecting arm having extending part, and a base part which is supported rotatably to the seatback and formed with ratchet teeth. The acceleration detecting mechanism includes a swinging member with a weight which is provided rotatably to the base part and has ratchet teeth. When inertia force occurring due to a crash of a vehicle from behind acts on the weight, the swinging member rotates and the ratchet teeth of the swinging member become engagement with the ratchet teeth of the base part. In this state, upon receipt of a seatback load of a passenger on the vehicle seat, the detecting arm rotates and this rotation transmits to the swinging member, which activates the headrest body to protrude frontwardly toward the passenger's head. Accordingly, when a vehicle is crashed from behind, the back of the passenger's head can be instantaneously received.
However, according to the above-described clutch mechanism, the rotation amount of the swinging member increases as the magnitude of seatback load from a passenger increases. Therefore, for example, when receiving the seatback load from a passenger of heavy weight, the swinging member might rotate more than necessary. In the case of a vehicle seat having a configuration in which the headrest body or the like is activated in response to an operation cable being pulled by the rotation of the swinging member, if the swinging member rotates more than necessary, the excessive tensile force is exerted to the operation cable.